What Geoengineering the World Could Mean for the Southwest
Geoengineering—the deliberate, planetary-scale alteration of the earth system—is being proposed more and more frequently these days as a way of combating global warming (recent articles in The Economist, Scientific American and Science provide a good overview).
One of the more popular geoengineering plans to reduce global warming is to inject sulfate aerosols in the stratosphere, mimicking the effects of volcanic emissions. Sulfur from large volcanic eruptions can enter the stratosphere. Once there, sulfate converts to sulfate particles, which reflect incoming sunlight back to space, cooling the earth’s surface. The most popular example of the impact of volcanic aerosols on earth’s climate is AD 1816, known as the “year without a summer.” The abnormally cool temperatures in North America, Europe, and elsewhere during this year were due to the colossal 1815 Tambora eruption in Indonesia.
Such cool temperatures are starting to appeal to those worried about the effects of global warming. Could we reduce the temperature of the planet by mimicking colossal volcanic eruptions like Tambora? Although the technology is currently not in place, modeling studies suggest that stratospheric sulfate aerosols would cool the planet—the sulfur aerosol equivalent of about one Pinatubo every four years would be needed to offset global warming (Robock, 2010). But should we? Are things bad enough, and are we scared enough to begin such a dramatic planetary experiment?
Modeling studies that simulate the impact of stratospheric sulfate aerosols also show many unintended consequences besides global cooling (Ammann et al., 2010; Robock et al., 2009; Robock et al., 2008). This list of benefits and risks from Robock et al. (2009) sums up the case for sulfate aerosol geoengineering pretty well:
What would happen in the Southwest if we did end up cooling the planet with sulfate aerosols? Nobody has tackled this specific question yet, but based on modeling experiments, temperatures would most likely go down. But our precipitation patterns could also change. There is evidence in modeling studies that stratospheric sulfate aerosols weaken the Earth’s hydrologic cycle. Right now, the hydrologic cycle is being enhanced by global warming, meaning the tropics are getting wetter and the dry subtropics, including the Southwest, are getting drier. So would this mean wetter conditions for the Southwest with sulfate aerosols?
A new study also shows that the influence of the tropical Pacific El Niño/Southern Oscillation phenomenon on climate around the world changes when we dim the sun (Braesicke et al., 2011). Since ENSO plays a critical role in Southwest precipitation, this change in ENSO teleconnections could have impacts on Southwest precipitation.
Unfortunately, a sulfate-filled stratosphere would also mean all the telescopes sitting on Arizona mountaintops would be useless, since the stars would be perpetually blotted out.
There are just so many uncertainties and risks associated with sulfate aerosol injection into the stratosphere. So are things bad enough to consider such a high-risk geoenginnering solution? My answer is no, they are not. Why don’t we focus our energy on safer solutions like geosequestration of CO2 and emissions reductions instead?